Accurately measuring the current load on a Mac

I'm trying to add a little feature that takes the current load on a computer and then sends it back to a central server (same computer or different computer it does not really matter) and then the server routes network requests based on the load of the registered servers with it.

What is the best way of getting current load on a Mac for a system such as this? It is a C only application I am afraid so no Cocoa / Objective-C.

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